This invention relates to fluoride-containing chromia-silica catalysts.
Supported chromium-containing catalysts can be used to prepare olefin polymers in a hydrocarbon solution to give a product having excellent characteristics from many standpoints. Supported chromium-containing catalysts can also be used to prepare olefin polymers in a slurry system wherein the polymer is produced in the form of small particles of solid material suspended in the diluent. This process, frequently referred to as a particle-form process, has the advantage of being less complex. However, there is substantially less leeway in controlling the ultimate properties of the polymer produced when using the particle-form process. For instance, one method of controlling molecular weight of the resulting polymer in the solution process is simply to vary the temperature, with lower molecular weight (high melt flow) polymer being produced at the higher temperature. It is readily apparent that this type of process control is severely limited in the particle-form process since any substantial increase in temperature would cause the polymer to go into solution. This problem is further complicated in the particle-form process when it is desired to produce a relatively narrow molecular weight distribution polymer having a relatively high melt flow.